Thus far, an optical disk that uses laser light to record information or reproduce recorded information has been in practical use. Types of the optical disk include a reproduction-only type, a recordable type, and a rewritable type. In the recordable type and the rewritable type, it is necessary that address information indicating positions of the optical disk be recorded in advance in order to record information.
As a method for recording address information, there is known a system in which a signal that forms a trench called a wobble is modulated in accordance with the address information. The trench is referred to as a groove, and a track formed by the groove is referred to as a groove track. The groove is defined as a portion irradiated with laser light during the manufacturing of the optical disk, the area sandwiched between adjacent grooves is referred to as a land, and a track formed by the land is referred to as a land track.
In general, when recording address information, a synchronization portion (hereinafter, referred to as a sync pattern as appropriate) and a data portion (hereinafter, referred to as address data as appropriate) are recorded. The position where the address information is recorded is found by means of the sync pattern, and the address data are reproduced. It is desirable for the sync pattern to be clearly distinguishable from the address data.
For example, in a Blu-ray Disc (BD) (registered trademark), address information is recorded by a wobble groove, and data are allowed to be recorded on the groove (see Patent Literature 1). As the system for modulating the address, both minimum shift keying (MSK) and a saw-tooth wobble (STW) are used in the BD.